Recently, from standpoint of saving natural sources and energy, small sizings and high efficiency of electromagnetic or electronic parts have been demanded, and soft magnetic property, especially Si steel sheets having excellent iron loss have been also required. It is known that soft magnetic properties of Si steel sheets are improved with increasing of addition of Si and exhibit the maximum permeability at about 6.5 wt %, and since natural electric resistance is high, the iron loss is made small. In this kind of steel sheets, if Si content is greater than 4.0 wt %, workablity is abruptly worsened, and therefore it has been impossible to produce high Si steel sheets in industrial scales by the rolling process, but it has been found that the warm rolling could be performed on the thin steel sheets.
For warm rolling (200.degree. to 600.degree. C.) this kind of steel sheets, it is important to perform rolling and lubricating as keeping the above mentioned temperatures for following purposes;
1) preventing a blank from crackings; PA0 2) reducing a rolling load because of large deforming resistance; and PA0 3) satisfying sheet surface property.
The warm rolling is carried out on nonferrous metals as Al. In this rolling, an oil is much applied to lubricate and cool the sheet. However it is very important that the high Si sheet should not be cooled. Surface pressure is very high in comparison with rolling on the nonferrous metals and the above mentioned lubrication is not suited to the warm rolling of the high Si steel sheet.
The lubrication of water soluble coolant is employed to hot rolling, but since this is to cool the steel materials and the rolls, such a lubrication could not be used to the warm rolling of the high Si steel. In cold rolling, the lubricant mixed with an oil and a water is sprayed, but such a lubrication cannot be used to the warm rolling, either, because the temperature of the steel is lowered thereby.
These conventional rolling lubrications could not be adopted to the warm rolling of the high Si steel sheet with less workablility, and a new lubricating way has been demanded for smooth warm rolling.